Heat transfer system applying boundary later penetration

ABSTRACT

A heat transfer system is disclosed incorporating a passive pump utilizing bubble technology to cycle a coolant through associated channels. The system includes a housing and channels containing a slurry consisting of liquid having a low boiling point and microspheres formed of metallic foam introduced into said liquid. The microspheres are caused to flow onto a heat source and penetrate the coolant boundary layer and thereby provide an efficient and fast transfer of heat from the source onto the microspheres and the coolant. The microspheres further provide and efficient and fast transfer of heat through the slurry to a heat dissipating component.

This application claims the benefit of the earlier filing date of theprovisional application Ser. No. 61/628,982 filed on Nov. 10, 2011 ofthe same title and of the same inventor, Troy W. Livingston.

BACKGROUND OF THE INVENTION

The present invention relates to a system and method for removing anddissipating heat from heat generating components such electronic chips,electronic circuit board and power components in computers.

This provisional patent application is related to U.S. PatentApplication Ser. No. 61/575,946 filed on Aug. 31, 2011 titled “HeatTransfer Bridge” in the name of Troy W. Livingston. Said provisionalapplication is being filed as a regular utility application concurrentlyherewith and is incorporated herein by this reference thereto. The Ser.No. of said utility application will be provided to the USPTO asavailable.

SUMMARY OF INVENTION

A heat transfer system is disclosed incorporating a passive pumputilizing bubble technology to cycle a coolant through associatedchannels. The system includes a housing and channels containing a slurryconsisting of liquid having a low boiling point and microspheres formedof metallic foam introduced into said liquid. The microspheres arecaused to flow onto a heat source and penetrate the coolant boundarylayer and thereby provide an efficient and fast transfer of heat fromthe source onto the microspheres and the coolant. The microspheresfurther provide a fast transfer of heat through the slurry to associatedheat dissipating components.

The foregoing features and advantages of the present invention will beapparent from the following more particular description of theinvention. The accompanying drawings, listed herein below, are useful inexplaining the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a section view of the inventive system depicting the formationof bubbles in a slurry comprising microspheres in a fluid wherein thebubbles are generated by a heat source and the interaction of thebubbles with microspheres to drive the slurry including the microspheresto and through the coolant outlet;

FIG. 2 is a highly enlarged view of a microsphere useful in describingthe penetration of the fluid boundary layer to provide an efficienttransfer of heat from the microsphere to the bounding metal surface;

FIG. 3 is useful in further explaining the efficient transfer of heatthrough the microspheres which effectively form a series of rapid heattransfer zones;

FIGS. 4A and 4B show a copper panel that is a material from which themicrospheres are formed;

FIG. 5 shows the initial operation for cutting the panel of FIG. 4A intorectangles to initiate the operation to make the microspheres;

FIGS. 6A, 6B and 6C show the succeeding operations for forming themicrospheres from the rectangle into a oval or circular form; and

FIG. 7 depicts an alternative embodiment of the invention wherein air isprovided as the microsphere carrying medium rather than a liquid.

DESCRIPTION OF INVENTION

As cited above, the present application is related to U.S. provisionalpatent application Ser. No. 61/575,946 filed on Aug. 31, 2011 titled“Heat Transfer Bridge” in the name of Troy W. Livingston. The content ofsaid Heat Transfer Bridge application is incorporated herein by thisreference and cites the need for systems and methods for coolingelectronic chips, electronic circuits, computers. Further discussions ofthe need for cooling electronic components is discussed in a multitudeof U.S. patents including for example the recent U.S. Pat. No. 8,011,424issued to Mark M. Murray and titled “Method for Convective Heat TransferUtilizing a Particulate Solution in a Time Varying Field”.

The afore cited Livingston patent application Ser. No. 61/575,946discloses cooling systems utilizing heat pumps and bubble technology toprovide cooling for electronic circuits, IC chips and computers. Patentapplication Ser. No. 61/575,946 also discloses the provision of acoolant comprising a slurry including formed metal particles, and thisapplication incorporates by reference thereto the disclosure anddrawings of said application. The present invention provides improvementto said application Ser. No. 61/575,946.

FIG. 1 depicts a heat transfer system 12 including a liquid container 14having a bubble forming chamber 16 all essentially indistinguishablefrom the embodiment shown in FIG. 30 of application Ser. No. 61/575,946.The formation, and initial function, of the bubbles 32 (and thesubsequent coalesced bubbles) is to provide a pumping action to powerthe flow of a fluid as disclosed in said application 61/575,946. Forpurposes of the present description only the bubble chamber 16 and theoutlet tube/channel 18 and return tube/channel 20 are shown in FIG. 1.The other section of the heat transfer system are shown and described inthe afore cited Ser. No. 61/575,946. A liquid slurry 30 that comprisesmicrospheres 26 that are introduced into a fluid 24 to provide anenhanced and rapid transfer of heat are basic concepts of the invention.

Container 14 is mounted over a heat source 22 comprising, for example,an IC chip. The adjacent sections of the overall system 12 includingcontainer 14 and outlet tube 18 and return tubes 20 are disclosed anddescribed in the referenced patent application, Ser. No. 61/575,946. Theimprovements provided by the present invention can be fully describedusing the relatively simplified drawings of FIGS. 1-3.

As disclosed in said prior application, a fluid such as for examplemethylene chloride 24 is contained in container 14 and in tubes 18 and20. Methylene chloride (dichloromethane) is a volatile fluid that has alow boiling point of 39.6 degrees C. (103 degrees F.). Note that otherfluids having a low boiling point could also be utilized. Microspheres26 are introduced into the fluid 24 to form a slurry 30 that can flow inthe tubes 18 and 20. As will be explained in more detail hereafter, in apreferred embodiment the copper microspheres are approximately 0.020inches in diameter and are formed of copper foam material. Note that inthe cited application Ser. No. 61/575,946 metal particles are employedin the slurry 30, whereas but in the present application comprisesformed foam copper microspheres 26 are introduced into the liquid 24 toconstitute the slurry 30.

Refer now briefly to the bubble function in chamber 16. When the heatsource becomes hot and the dichloromethane fluid 24 reaches its boilingpoint of 103 degrees F., the fluid will start to produce bubbles 32 onthe interior surface 34 of chamber 16 which is adjacent the heat source22. The small originating bubbles 32 will rise and coalesce continuouslyto form larger bubbles 36, and the still larger bubbles indicated at 38.The coalescing function indicated in FIG. 1 may occur several times andis dependent on the fluid parameters, the temperature, the size ofchamber 16, etc. Chamber 16 is shaped to guide the bubbles upwardlytoward outlet tube 18. It has been found that all the bubbles 32, 36 and38 push the hot slurry 30 including the hot fluid 24 and microspheres 26upwardly toward outlet tube 18, as indicated by the arrow linesgenerally labeled 17. Tube 18 is 3.5 mm in diameter which isapproximately the same diameter of the larger bubbles 38 in chamber 16.Since the larger bubbles 38 are approximately the same diameters as thetube 18, these bubbles effectively pump (push) the slurry 30 includingthe microspheres 26 through tube 18 (as indicated by the arrow line 21)and to the other sections of heat transfer system 12 as shown in FIG. 30of said application Ser. No. 61/575,946. As described in said citedapplication, the heated slurry 30 flows to and through a heat absorbing(heat dissipating) structure which may include radiating fins enablingthe slurry to transfer heat to the heat absorbing structure anddissipate heat energy in that region. The cooled slurry 30 than flowsback through return tube/channel 20, as indicted by arrow line 40 inFIG. 2, and returns to the bubble chamber 16 to be recycled.

FIG. 2 depicts a microsphere 26 of FIG. 1 in a highly enlarged view.FIG. 2 is useful in explaining the interaction of the microsphere withan associated heat source of heat dissipating (cooling) surface 34. Fordescription purposes, microsphere 26 is shown in an instantaneoussupported position on surface 34. Note of course, that the slurry 30including the liquid 24 and microspheres 26 are in a continuous flowmode during the operation. Importantly, the microsphere 26 is shown aspenetrating the fluid coolant boundary layer 42. The action of themicrospheres 26 to pierce the fluid coolant boundary layer is a basicfeature of the present invention.

A fluid boundary layer is a known phenomena in fluid mechanics and is alayer of substantially static fluid liquid 24 in the intermediate theflowing liquid and a bounding surface. The bounding surfaces shown inFIG. 1 comprise the interior surface of chamber 16, the interiorsurfaces of the tubes 18 and 20. For present purposes, the boundarylayer comprises a static thin film of liquid that is next to the surfacewalls of the liquid containment surface and acts as an insulator thuspreventing the heat energy in the bounding surface to efficientlytransfer heat to the flowing liquid through the heat conducting surface.This reduction in the heat transfer is detrimental in both theabsorption of heat from the heat source and the dissipation of heat tothe heat radiating components. Fluid viscosity and fluid flow rateaffect the boundary layer thickness and the resulting heat insulatingeffect. Prior liquid cooling systems depend on liquid flow to providethe cooling medium are subject to a loss in efficiency due to theeffects of the liquid boundary layer phenomena. The present inventionsolves the problem.

The inventive cooling system disclosed herein provides microspheres offoamed metal that are introduced into a cooling liquid to form a slurry.The microspheres are formed into round balls and compressed to match thedensity of the liquid to provide an almost neutral buoyancy to provide aunique heat transfer slurry. The microspheres penetrate the boundarylayer as will be described herein to improve the heat transfer rate andthe heat transfer efficiency. As alluded to above, the heat transferrate and as well as the heat transfer efficiency are improved both whentransferring heat to the microspheres from a hot source and whentransferring heat from the microspheres to a heat dissipating source.

In a preferred embodiment, microspheres 26 are formed from copper foam.Copper is an excellent conductor of heat. The microspheres areintroduced into a methylene chloride liquid 24 to form the coolantslurry 30. In one embodiment, the slurry 30 comprises forty percent byvolume of methylene chloride 24 and forty percent by volume of foamcopper microspheres 26; other fluids having a low boiling point may beused. The boundary layer as specifically related to the presentinvention will now be described with reference to FIG. 2.

For purposes of description and clarity FIG. 2 depicts a highly enlargedview of a single microsphere 26 positioned on the liquid boundingsurface 40 of a heat source 34. The quantity of microspheres 26 in theliquid 24 is determined by various factors such as the thickness andflow rate of the slurry 30 desired, the heat transfer rate desired, etc.The coolant boundary layer 42 is depicted as a thin film and thethickness thereof is dependent on various factors including theviscosity of the coolant and the flow rate.

It is a function of the microspheres 26 to absorb heat from the heatsource 34; however as described above, the coolant boundary layer 42acts as an insulator tending to prevent heat transfer from the hotsurface 34 to the liquid slurry 30. Refer now to both FIGS. 1 and 2. Theslurry 30 containing the microspheres 26 flows back or returns to thebubble chamber 16 as indicated by the arrow line 40. The texturedsurfaces 46 of the copper microspheres 26 flow onto, engage, rub andscrape the bounding surface layer 42 and penetrate the boundary layer toprovide direct or full/good copper microsphere 26 to metal 34 contact asdepicted in FIG. 2. The thickness of the coolant boundary layer (theinsulator) is thus breached and effective metal to metal contact forheat transfer is thus accomplished. These actions results in anefficient and maximal high rate of heat transfer from the heat source 34directly to the microsphere s 26. The microspheres further transfer heatenergy to the surrounding liquid 24 and other microspheres in slurry 30.

Another important aspect of the invention is the improved rate of heattransfer provided by the copper microspheres in the slurry liquid ascompared to the rate of heat transfer in a clear liquid. As is known,the rate of heat conduction through a metal is much higher than inliquid. For comparison, thermal conductivity charts show that the heattransfer rate of copper given as 385 (W/mK) as compared to that of waterwhich given as 0.6 (at 20 degrees C.). As stated above the microsphere26 is formed from foamed copper material. The foamed copper iscompressed to the density of the coolant liquid, and since themicrosphere 26 is not solid copper, but rather a foam composite, therate of heat transfer through the microsphere can be considered tochange (as a rough approximation) to about 100 times the rate of heattransfer through the coolant liquid.

Refer now also to FIGS. 1 and 3. As evident from the drawings of FIGS. 1and 3 there is a multitude of microspheres in the slurry 30. FIG. 3pictorially and simplistically depicts the increased rate of heattransfer through the slurry 30 comprised of microspheres 26 and theliquid 24. Assume for description purposes a steady state and momentarycondition and that the boundary layer 42 of heat source 34 has just beenpenetrated by the microsphere 26A and the microsphere 26A rapidlyabsorbs the heat energy. As stated above, there is a fast rate of heattransfer through microsphere 26A that is about 100 times the rate ofheat transfer through the liquid 24. Next the heat energy frommicrosphere 26A exits upwardly into the liquid 24. There is a slowerrate of transfer of heat energy through the liquid 24 to the microsphere26B. Next there is a rapid transfer of heat through microsphere 26Bwhich is 100 times faster (indicated as 100×) than the transfer throughthe liquid. Microsphere 26B transfers energy to the surrounding liquid24. There is a slower rate of transfer of heat energy through the liquid24 to microsphere 26C. Next, there is a rapid transfer of energy throughmicrosphere 26C to the surrounding liquid 24. The surrounding liquidthan conveys the heat to the dissipating surface 48. Accordingly aseries of rapid heat transfer zones are formed in the coolant. The rateof heat transfer and the efficiency of heat transfer are thussignificantly enhanced as compared to that provided by a clear liquid.

Refer now to FIGS. 4A-4B that depict a procedure for forming the coppermicrospheres of the invention. While other metals such as aluminum canbe used in the inventive system, copper has been found to be thepreferred metal because of its better heat conductivity properties.FIGS. 4A and 4B show a copper sheet/panel 50 that is a material fromwhich the microspheres 26 are formed. FIG. 5 shows the initial operationsuch as a steel rule die 54 for cutting a sheet 50 of FIG. 4A intorectangular pieces/cubes 56 see FIG. 6A, to initiate forming themicrospheres 26. FIGS. 6A, 6B and 6C show the succeeding operations fortrimming the rectangular/cube 56 to form oval or circular microsphere 26and to compress the foam microspheres to a desired density for use asdescribed above. It should also be understood that microspheres ofdiffering sizes can be employed in the same slurry.

FIG. 7 depicts an alternative embodiment of the invention wherein air isprovided as the microsphere carrying medium rather than a liquid. Asdepicted in FIG. 7 microspheres 26 are fed through a tube 60 to exitadjacent and air nozzle 62. The air 64 from nozzle 62 has previouslypassed adjacent a heat source and is hot. The hot air 64 from the nozzledrives the microspheres 26 onto a heat dissipating surface 66. Theheated microspheres 26 penetrate the air boundary layer 68 of the heatdissipating surface and 66 and efficiently transfer heat to surface 66.The microspheres 26 which have dissipate their heat energy are thenreturned to a containing chamber as depicted by arrow line generallylabeled 69 for reuse.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

1. A heat transfer system comprising in combination a) a container for aflowing fluid slurry, said container having a panel with an interiorbounding surface for said slurry and an exterior surface for receivingheat wherein a fluid boundary layer comprising a thin film of fluidformed on said bounding surface effectively comprises a heat transferinsulator; b) an outlet channel and an inlet channel for said container;c) a slurry comprising a fluid having a low boiling point and metalmicrospheres; d) a heat source positioned to be thermally coupled tosaid container; e) said fluid generating bubbles in response to heatreceived from said heat source; f) said bubbles providing a pumpingaction to drive said heated slurry upwardly through said outlet channele) a large quantity of said metal microspheres in said slurry beingmoved over and engaging said interior bounding surface therebypenetrating said fluid boundary layer to obtain an efficient metal tometal heat transfer.
 2. A fluid flow system for transferring heat from aheat source to a heat dissipating region, said system comprising incombination a) a container inclosing a flowing liquid slurry; b) a heatsource mounted to provide heat to said container and said slurry; c)said slurry containing a plurality of foamed copper microspheres thatare substantially of the same density as said liquid; d) said fluidgenerating bubbles in response to heat received from said heat sourceand said bubbles providing a pumping heated slurry to flow from saidheat source toward said heat dissipating region and said microspheres totransfer heat generally upwardly and away from said heat source; e) saidcopper microspheres in said flowing providing a fast rate of heattransfer through the spheres to adjacent liquid, said liquid slurryproviding a slower rate of heat transfer to adjacent microsphere whichnext provides a fast rate of heat transfer to adjacent microspheres andliquid whereby a series of zones of fast heat transfer are provided tothereby in total effect a fast efficient transfer of heat from said heatsource to said heat dissipating region.
 3. A heat transfer systemcomprising in combination a) a source of metallic microspheres; b) asource of heated air; c) a heat dissipating surface; d) a chamber regioninto which said microspheres are introduced; e) a nozzle for jettingsaid heated air into said chamber region and to impinge on said heatdissipating surface; f) said jetted heated air driving said microsphereonto said heat dissipating surface and penetrating the air (fluid)boundary to provide a fast rate of heat transfer from said heated air tosaid dissipating surface.
 4. A heat transfer system as in claim 1wherein a) a portion of said flow path is angled causing saidmicrospheres to strike against said interior boundary layer surface. 5.A heat transfer system as in claim 1 providing a relatively enlargedheating chamber enabling said bubbles to coalesce to the size of saidoutlet channel to drive said bubbles through said channel.